Pyramid and Sand Twister
May 06, 2010
The photo above shows a whimsical whirlwind at the base of the Pyramid of Khephren on the Plateau of Giza in Egypt. It was taken on the Vernal Equinox (March 20, 2010). Cold gales were blowing over the Plateau much of the day. As I was observing the setting Sun on the eastern flank of the Plateau of Giza, I noticed this swirl of wind, made visible by the sand it entrained. Whirlwinds or dust devils form under clear skies beneath a weak updraft, unlike tornadoes, which take shape in unstable air displaying strong updrafts and wind shear. Though their size may vary considerably, most of these whirlwinds have diameters that range from approximately 10 ft (3 m) to 100 ft (30 m), and they last usually no more than a few minutes. Note that the date of the equinox and the formation of this eddy are entirely coincidental.